NGC 2175 (Emission Nebula) & Pismis 27 (Open Cluster) in Orion
Monkey Head Nebula
The Emission Nebula NGC 2175 (Monkey Head Nebula) was the highlight of the night. This
moon-sized nebula was not at all difficult in the 110mm refractor on a very transparent night
at a local Park. Its full extent was helped with a OIII nebula filter. NGC 2175 is part of a larger
Emission (H-II Region) Nebula called Sharpless 2-252. The glow of the nebula is fueled mostly
by a Spectral Type O6.5V, magnitude 7.6 star (HD 420888) in the center of the nebula.
There is a lot of confusion in the names associated with the Monkey Head Nebula. Many star
atlases identify the nebula as NGC 2174 and not NGC 2175. The naming of the Open Clusters
associated with the Emission Nebula is a mess. Often the Open Cluster is called Collinder 84
(large) and includes most of the stars seen within the Monkey Head Nebula proper. The
so-called cluster also has been assigned erroneously as NGC 2175. Regardless of the name
it is likely a collection of up to ten individual star groups and thus does not exist as a true Open
Cluster. It clearly does not appear cluster-like in my small refractor. A much smaller Open
Cluster (Pismis 27) can be found at the northeastern edge of the Monkey Head Nebula. This
cluster also goes by NGC 6882 or Collinder 84 (small), but both names are in dispute.
I find it best to just ignore the nomenclature and just enjoy the view. This is one fine complex
object and one that is under appreciated by many amateur astronomers.